SF 


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U.    .     .     .    GIr.    .  47. 


list    1919. 


UC-NRLF 


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Agric-.fr  ores!  library 


BIOLOGY 

LIBRARY 

G 


STOMACH  WORMS  IN  SHEEP 

PREVENTION  AND  TREATMENT 


Prepared  Jointly  by  the  Animal  Husbandry 
and  Zoological  Divisions 


UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 
DEPARTMENT  CIRCULAR  47 


Contribution  from  the  Bureau  of  Animal  Industry 
JOHN  R.  MOHLER,  Chief 


Washington,  D.  C.  August,  1919 


WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  :  1919 


•  • .  - 


*ioic. 


STOMACH  WORMS  IN  SHEEP: 

PREVENTION  AND  TREATMENT. 


CONTENTS. 

Page. 

How  can  one  tell  when  sheep  have  stomach  worms  ? 3 

How  do  the  worms  injure  the  sheep ? 4 

How  should  infested  sheep  or  lamhs  be  treated  ? 4 

How  do  sheep  become  infested  by  stomach  worms  ? 6 

What  methods  can  be  employed  to  prevent  loss  from  stomach  worms ? 8 


ONE  of  the  most  serious  problems  of  owners  of  farm  sheep  is  the 
prevention  of  injury  and  loss  by  stomach  worms.  This  para- 
site (Hxmonchus  contortus)  has  been  known  in  this  country  for  many 
years  and  is  common  in  farm  flocks,  particularly  during  wet  summers. 
It  has  been  studied  bv  the  Zoological  Division  of  the  Bureau  of 
Animal  Industry  and  the  principal  facts  in  its  life  history  have  been 
determined.  Methods  of  treatment  and  of  prevention  are  still  under 
investigation  by  that  division,  and  although  the  methods  have  not 
yet  been  perfected,  what  has  been  learned  is  sufficient  to  show  how 
affected  sheep  or  lambs  can  be  treated  successfully  and,  what  is  of 
greater  importance,  how  they  may  be  raised  in  such  a  way  as  practi- 
cally to  overcome  the  danger. 

What  is  known  of  this  parasite  and  the  methods  of  prevention  and 
control  may  be  presented  as  answers  to  practical  questions,  as 
follows : 

HOW  CAN  ONE  TELL  WHEN  SHEEP  HAVE  STOMACH  WORMS? 

Either  lambs  or  old  sheep  may  be  affected  by  stomach  worms  at 
any  time  of  the  year.  The  trouble  may  be  noticed  first  in  lambs 
about  the  middle  of  summer,  though  it  may  be  earlier,  according  to 
the  part  of  the  country  and  the  temperature  and  moisture  of  the 
season. 

In  many  flocks  the  first  knowledge  of  the  trouble  is  gained  through 
the  death  of  one  or  more  lambs.  If  the  flock  is  under  careful  obser- 
vation, however,  signs  of  stomach-worm  disease  will  be  noticed 
earlier.  Dullness  and  lack  of  thrift  are  among  the  first  indications. 
Scouring  is  often  present.  These  conditions  may  result  from  other 
causes,  but  when  due  to  stomach  worms,  they  are  accompanied  with  a 
very  pale,  bloodless  appearance  of  the  skin  and  of  the  mucous  mem- 
branes of  the  eyes  and  mouth.  The  whiteness  of  the  skin  has  caused 
the  trouble  to  be  known  in  some  sections  as  "paper  skin."  In  many 
cases  there  is  a  watery  swelling  under  the  jaws. 

120227°— 19  3 

4< 


■      •    • 

•  ■•■    :  :•  :  • 


4     Departnu'it  Cx'r£WdK|f,  T$J$.  Department  of  Agriculture. 

Doubt  as  to  the  cause  of  the  trouble  ran  be  removed  by  an  exami- 
nation of  the  fourth  stomach.     For  examination  purposes,  any  one 

unfamiliar  with  the  ailment  can  well  afford  to  kill  an  affected  lamb. 
If  there  is  any  uncertainty  as  to  the  position  of  the  fourth  stomach 
it  can  be  ascertained  by  taking  hold  <»f  any  part  of  the  -mall  intestine 
and  following  it  forward.  The  fourth  stomach  is  one  of  the  4  com- 
partments into  which  the  stomach  is  divided  ami  i-  the  portion  con- 
tinuous with  the  forward  end  of  the  -mall  intestine.  When  the 
fourth  stomach  is  found,  it  should  be  held  bo  .1-  to  prevent  the 
fluids  from  leaving  it  at  either  end,  and  an  incision  made  along 
nearly  the  full  length  of  the  upper  part.  When  this  is  done  the 
stomach  worms,  if  present,  can  be  seen,  often  in  large  numbers, 
wriggling  around  in  the  fluids.  They  are  from  one-half  to  1}  inches 
long,  about  as  thick  as  an  ordinary  pin,  and  spirally  striped  with 
red  and  white.  It  is  often  necessary  to  look  closely  for  some  time 
in  order  to  distinguish  them.  When  the  stomach  is  emptied  some 
of  the  worms  can  be  seen  adhering  to  the  inside  walls. 

HOW  DO  THE  WORMS  INJURE  THE  SHEEP? 

The  injurious  action  of  the  stomach  worms  may  be  attributed  to 
two  things:  First,  the  loss  of  blood  abstracted  by  the  parasites,  and 
second,  the  destruction  of  red  corpuscles  by  a  poisonous  substance 
which  is  secreted  by  the  parasites  and  taken  up  by  the  blood.  Evi- 
dently the  older,  stronger,  and  larger  sheep  are  better  able  than  the 
lambs  to  withstand  the  loss  of  blood,  and  can  better  endure  the  I 
duo  to  the  destruction  of  red  corpuscles.  Furthermore,  in  the  blood 
of  adult  sheep  there  may  be  substances  tending  to  neutralize  the 
poisonous  matter  produced  by  the  parasites  that  are  absenl  from  the 
blood  of  lambs,  or  that,  if  present,  occur  in  smaller  quantities. 
Besides  the  direct  injury  caused  by  stomach  worms  it  is  nof  unlikely 
that  damage  is  also  done  by  bacterial  infection  through  the  wounds 
the  worms  make  in  the  mucous  lining  of  the  stomach. 

HOW  SHOULD  INFESTED  SHEEP  OR  LAMBS  BE  TREATED? 

MEDICINAL  TKi:  A  I  U  INT. 

[f  taken  in  time,  most  cases  of  stomach  worms  can  be  treated 
successfully  according  to  the  following  directions: 

Dissolve  one-fourth  pound  (avoirdupois)  of  the  powdered  crystals 
of  copper  Bulphate  (bluestone)  in  I  pint  of  boiling  water,  using  a 
porcelain  or  enamel-ware  di  h,  as  the  Milestone  corrodes  most  metals. 

Then    add    cold    Wiiler   enough    to   make    the  solution    up    to   ;;   gallons, 

using  Wooden,   cart  lienw  ale,   or  other   iinelallic    recept  acles.      This 

will  make  approximately  a  I  percent  solution  and  will  be  enough  to 
(lose  1(H)  adult  sheep,  allowing  Id  per  rent   u  a    le.       In  the   preparation 

of  the  dose  use  onlj   clear-blue  crystals  of  copper  sulphate.     Crush 

the  crystal     to  a   line  powder  when   reads    to  make  up  (he  solution. 


Stomach  V/orms  in  SJieep.  5 

The  doses  for  lambs  and  sheep  are : 

For  lambs  under  1  year  of  age 1|  ouncea  (50  cubic  centimeters). 

For  sheep  past  1  year  old 3$  ounces  (100  cubic  centimeters). 

A  glass  with  marks  scratched  on  the  side  with  a  file  may  be  used 
for  measuring  the  doses. 

The  drenching  apparatus  consists  of  (1)  a  strong  rubber  tube 
about  3  feet  long  and  three-eighths  inch  in  diameter;  (2)  a  hard  rubber, 
porcelain,  or  enamel-ware  funnel,  which  is  fastened  to  one  end  of 
the  tube;  and  (3)  a  brass  mouthpiece  three-eighths  inch  in  diameter 
and  9  inches  long,  fastened  to  the  other  end.  It  is  preferable  that 
the  end  of  this  tube  should  be  closed  and  holes  made  in  the  sides  of 
about  the  last  two  inches  of  its  length. 

Ordinarily  the  treatment  is  given  after  the  sheep  have  been  without 
feed  overnight,  but  apparently  it  may  be  given  with  equally  good 
results  without  preliminary  fasting,  provided  the  animals  are  not 
gorged  with  feed  or  water  when  treated.  For  best  results  sheep 
should  not  be  watered  for  2  hours  afterwards. 

While  being  drenched  the  sheep  should  remain  on  all  4  legs  with 
its  head  held  horizontally.  This  is  important,  for  if  the  head  is 
held  above  the  horizontal  (nose  higher  than  the  eyes),  there  is  danger 
that  some  of  the  fluid  will  pass  into  the  lungs,  thereby  causing 
pneumonia  and  almost  certain  death.  Measure  the  dose  in  the 
measuring  glass,  and  after  the  drenching  tube  is  in  position  pour  the 
dose  slowly  into  the  funnel.  The  metal  mouthpiece  of  the  drenching 
tube  should  be  placed  between  the  jaws  in  the  space  between  the 
teeth  at  the  side  of  the  mouth  and  directed  backward,  but  should 
not  reach  farther  than  the  base  of  the  tongue.  In  order  to  prevent 
the  sheep  from  stopping  up  the  end  of  the  mouthpiece  with  its 
tongue  and  thus  interfering  with  the  flow  of  the  liquid,  the  person 
holding  the  mouthpiece  in  the  sheep's  mouth  should  give  it  a  rotary 
motion.  This  tends  to  keep  the  sheep  swallowing,  prevents  plugging 
the  tube,  and  also  tends  to  keep  the  fluid  from  entering  the  lungs. 
The  fluid  should  not  be  administered  more  rapidly  than  the  sheep 
can  swallow  comfortably. 

Care  in  the  administration  of  the  dose  is  highly  important,  as 
carelessness  or  any  undue  haste  is  liable  to  have  serious  results. 
The  copper-sulphate  treatment,  like  the  administration  of  medicines 
in  general,  is  safest  in  the  hands  of  a  competent  veterinarian. 

CHANGE  OF  PASTURE  NECESSARY  FOR  BEST  RESULTS. 

Although  losses  from  stomach  worms  in  many  cases  may  be 
minimized  by  repeated  medicinal  treatment  without  change  of 
pasture,  much  better  results  can  be  obtained  if  the  treated  animals 
are  placed  on  ground  that  is  free  or  practically  free  from  infection. 
It  is  still  better  to  institute  preventive  measures  before  the  results 
of  stomach-worm  infection  become  evident.     A  lamb  that  has  been 


.    ■ 


■ 


6     DcpartiHi'iU ",  '.inuilup  'il ,  V/S.  Department  of  Agriculture. 

affected  sufficiently  to  show  the  external  effects  of  stomach  worms 
has  received  a  serious  setback.  Although  it  may  recover  and  again 
be  thrifty  it  has  lost  at  least  a  month  or  6  weeks  of  progress  toward 
marketable  weight  and  condition.  The  only  safe  and  economical 
way  of  raising  sheep  where  stomach  worms  are  a  factor  is  by  managing 
the  flock  and  pastures  in  a  way  to  prevent  a  serious  develop- 
ment of  the  trouble.  In  most  localities  the  methods  necessary  for 
preventing  stomach  worms  are  at  the  same  time  those  that  need 
to  be  employed  for  most  economical  production.  In  order  to  follow 
these  methods,  particularly  with  respect  to  pasture  rotation,  the 
shepherd  needs  to  know  just  how  and  when  infection  occurs. 

HOW  DO  SHEEP  BECOME  INFESTED  BY  STOMACH  WORMS? 

INFESTED  PASTURES. 

In  the  adult  sexual  stage  stomach  worms  are  able  to  live  and 
carry  out  their  reproductive  functions  only  in  the  alimentary  canal 
of  sheep  or  other  ruminants,  and  practically  only  in  the  fourth  stom- 
ach. Each  female  produces  thousands  of  eggs,  of  microscopic  size, 
which  do  not  develop  into  adult  worms  in  the  body  of  the  host  in 
which  they  are  deposited,  but,  without  hatching,  pass  out  of  the 
intestine  in  the  feces.  In  a  few  hours,  days,  or  weeks,  according  as 
the  temperature  is  high  or  low,  these  eggs,  if  they  are  not  killed  by  dry- 
ing or  freezing  (either  of  which  is  commonly  fatal  to  them),  hatch  and 
the  tiny  embryonic  stomach  worms  then  develop  to  what  may  be 
termed  the  final  larval  or  infectious  stage.  This  later  development  like- 
wise requires  days  or  weeks,  according  to  the  temperature,  and  until 
the  young  worms  have  reached  the  infectious  stage  they  appear  to  be 
fully  as  susceptible  to  freezing  and  drying  as  the  eggs.  Having 
reached  the  infectious  stage,  however,  the  worms  are  able  to  with- 
stand long  periods  of  dryness  and  severe  cold,  though  some  of  them 
succumb  comparatively  early. 

In  the  infectious  stage  the  young  worms  are  very  active  in  the 
presence  of  moisture,  and  rapidly  orawl  up  blades  of  grass  and  other 
objects  whenever  the  relative  humidity  of  the  air  is  at  a  maximum, 
provided  the  temperature  is  above  40°  F.  or  thereabout;  below  that 
temperature  they  are  inactive.  A  decrease  in  the  relative  humidity, 
with  the  consequent  evaporation  of  the  moisture  from  the  surface  of 
grass  blades  and  oilier  objects,  Btops  (lie  migrations  of  the  worms, 
and  they  become  quiesoent  and  remain  in  a  condition  of  suspended 
animation  \\  herever  they  happen  to  be  at  the  time.  During  (be  next 
period  of  wet  weather,  dew,  rain,  or  fog,  the  worms  again  become 
active  ami  climb  still  Idgber  on  the  grass,  from  winch  thej  are  better 
able  to  attain  their  final  abode  within  the  stomach  of  a  sheep  or  row 
than  if  they  remained  on  the  ground.  When  swallowed  by  a  sheep 
or  other  ruminant  the  young  stomach  worm,  if  il  has  reached  its  fmal 


Stomach  Worms  in  Sheep.  7 

larval  stage,  whether  active  at  the  time  or  in  a  state  of  suspended 
animation,  continues  its  development,  and  in  the  course  of  2  or  3 
weeks  reaches  maturity. 

The  length  of  life  of  individual  worms  in  the  stomach  has  not  been 
determined.  Infested  sheep  have  been  kept  in  pens  with  board 
floors,  which  were  kept  clean  by  sweeping  and  frequent  scrubbing — 
the  sheep  being  fed  from  raised  racks  and  water  being  supplied  in  a 
trough  which  was  frequently  cleaned — for  varying  periods  up  to  a 
maximum  of  19  months,  and  at  the  end  of  these  periods  were  found 
to  be  still  infested,  though  the  number  of  worms  present  was  small. 

As  the  possibility  of  reinfection  by  larval  worms  developing  from 
eggs  passed  in  the  feces  of  these  sheep  was  not  entirely  removed, 
though  greatly  minimized,  the  results  obtained  do  not  necessarily 
indicate  that  the  worms  found  at  the  end  of  the  period  of  observation 
were  all  present  when  the  experiment  was  begun.  The  experiment, 
however,  while  it  proves  nothing  as  to  the  length  of  life  of  the  adult 
stomach  worm,  demonstrates  the  futility  of  attempting  to  rid  sheep 
entirely  of  stomach  worms  simply  by  keeping  them  away  from  pas- 
ture. On  the  other  hand,  very  little  infection  occurs  among  sheep 
kept  in  stables  if  cleanly  conditions  are  maintained.  Lambs  have 
been  kept  with  infested  sheep  in  stables  for  long  periods  of  time,  the 
only  precautions  against  infection  being  the  removal  of  manure  about 
once  a  week.  Under  such  conditions  they  have  continued  in  good 
health,  and  acquired  only  a  very  few  stomach  worms  and  other 
parasites. 

LENGTH  OF  TIME  PASTURES  MAY  BE  INFESTED. 

The  maximum  period  during  which  the  larval  stomach  worms  are 
able  to  survive  on  pastures  is  not  definitely  known,  but  it  has  been 
found  that  pastures  on  which  infested  sheep  had  grazed  were  appar- 
ently still  infectious  after  a  lapse  of  nearly  8  months,  namely,  from 
October  25,  when  the  infested  sheep  were  removed,  to  June  16,  when 
the  pastures  were  tested  by  placing  in  them  some  lambs  which  had 
been  raised  under  special  precautions  to  avoid  previous  infestation. 
In  cultures  made  September  14,  1906,  from  the  feces  of  an  infested 
sheep  and  kept  thereafter  in  the  laboratory,  most  of  the  larvae  were 
dead  but  some  were  still  alive,  though  very  sluggish,  on  June  5,  1907, 
nearly  9  months  later.  Cultures  in  which  the  worms  were  allowed 
to  develop  to  the  final  larval  stage,  after  they  were  kept  in  cold  storage 
at  a  temperature  below  freezing — in  some  cases  as  low  as  12°  F. — 
still  contained  some  living  worms  after  2  or  3  months,  while  in  other 
cultures  eggs  and  newly  hatched  worms  not  yet  developed  to  the  final 
larval  stage  were  killed  within  a  few  hours  after  exposure  to  tempera- 
tures below  freezing. 

These  experiments  show  that  pastures  may  remain  infected  for 
several  months  after  sheep  are  removed  from  them,  and  that  the 


8     Department  Circular  47,  U.  S.  Department  of  Agriculture. 

infection  is  not  destroyed  by  cold  weather.  They  show,  however, 
that  during  a  winter  with  more  or  less  freezing  weather  there  is 
likely  to  be  little  or  no  increase  in  the  amount  of  infection  in  pastures 
occupied  by  infested  sheep.  The  eggs  passed  in  the  feoes  of  the  sheep 
will  either  be  killed  at  onoe  by  freezing,  or,  on  account  of  low  tem- 
peratures above  freezing,  will  remain  dormant  or  develop  so  slowly 
that  they  are  killed  later  by  frost  before  they  have  reached  the  final 
larval  stage,  which  is  resistant  to  cold.  At  the  same  time,  while  the 
infestation  of  pastures  may  not  be  increased  during  the  winter,  the 
infestation  of  the  sheep  may  be  added  to  by  their  picking  up  from 
time  to  time  larval  worms  which,  prior  to  the  beginning  of  cold 
weather,  had  developed  already  to  the  stage  in  which  they  are  able 
to  withstand  freezing. 

If  sheep,  goats,  and  cattle  are  kept  off  a  pasture  for  a  year,  it  is 
fair  to  assume,  upon  the  basis  of  our  present  knowledge,  that  all,  or 
practically  all,  larval  stomach  worms  will  have  died  within  that  time. 
There  is  also  little  doubt  that  the  period  required  for  the  practical 
disinfection  of  a  pasture  may  be  shortened  considerably  by  plowing 
it  and  placing  it  under  cultivation. 

Thus  there  are  two  ways  by  which  a  pasture  may  be  freed  of  infesta- 
tion, one  by  excluding  sheep  or  other  ruminants  for  at  least  a  year,  and 
the  other  by  turning  it  into  a  cultivated  field.  In  view  of  the  fact 
that  sheep  placed  on  disinfected  fields  or  pastures  probably  will  not 
be  entirely  free  from  infestation,  it  is  not  of  much  consequence 
whether  every  larval  stomach  worm  in  the  pastures  is  dead  or  not. 
The  approximation  to  this  point,  which  is  attained  by  vacating  pas- 
tures for  a  year  or  by  plowing  them  up,  is  sufficient  for  practical 
purposes. 

WHAT  METHODS  CAN  BE  EMPLOYED  TO  PREVENT  LOSS  FROM 

STOMACH  WORMS? 

It  is  barely  possible  that  some  means  of  artificially  producing  in 
lambs  an  immunity  against  the  evil  effects  of  stomach  worms  may 
be  devised,  but  at  the  present  time  it  is  only  a  matter  for  speculation 
and  experimental  research.  Our  present  knowledge  of  the  stomach 
worm  leads  us  to  direct  our  efforts  toward  bringing  about  freedom 
from  infestation  or,  as  the  next  best  thing,  reducing  the  amount  of 
infestation  to  a  minimum  and  keeping  it  there. 

EARLY  DEVELOPMENT  OF  LAMBS. 

One  great  step  toward  evading  the  stomach  worm  is  found  in  the 
plan  of  having  lambs  dropped  early  and  feeding  to  develop  them  as 
much  as  possible  before  they  go  to  pasture. 

Where  sheep  graze  during  winter  and  spring  there  is  little  danger 

of  infestation  in  freezing  weather,  as  the  eggs  or  young  larva'  are  killed 


Stomach  Worms  in  Sheep.  9 

before  they  are  taken  up  by  the  lambs.  There  is  but  very  slight 
danger  that  young  lambs  will  become  affected  seriously  while  running 
with  older  sheep  in  barns  or  yards  free  from  vegetation.  Early  lamb- 
ing, combined  with  good  feeding  of  the  ewes  to  make  them  milk  well, 
or  of  the  lambs  themselves  in  a  "  creep,"  or  with  both,  brings  early 
lambs  to  marketable  weight  and  finish  before  the  most  dangerous 
part  of  the  summer.  Where  lambs  must  remain  for  several  months 
on  pasture,  frequent  changing  of  pasture  must  be  resorted  to,  to 
keep  infestation  below  the  extent  that  is  injurious. 

A  PRACTICABLE  METHOD  OF  PASTURE  ROTATION. 

The  means  of  preventing  the  stomach-worm  larvae  from  getting 
into  the  lambs  is  suggested  by  what  has  been  said  concerning  its 
development  and  powers  of  resistance.  It  was  stated  that  a  pasture 
that  had  been  occupied  by  wormy  sheep  would  need  to  be  for  at 
least  a  year  without  cattle,  sheep,  or  goats  in  order  to  become 
practically  free  from  stomach-worm  larvae. 

From  10  to  20  days,  according  to  temperature  and  moisture,  must 
intervene  between  the  dropping  of  the  feces  containing  stomach- 
worm  eggs  and  the  development  of  many  of  the  larvae  to  a  point 
where  they  will  develop  into  adult  worms  after  being  swallowed.  If 
sheep  are  moved  to  a  fresh  pasture  before  the  eggs  in  their  droppings 
develop  into  mature  larvae,  complete  health  can  be  maintained.  The 
practical  difficulty  lies  in  always  having  a  fresh  pasture  available. 
If  only  permanent  grass  pasture  were  used,  adequate  control  would 
call  for  as  many  separate  pastures  as  would  allow  the  flock  to  be 
moved  at  least  every  2  weeks  without  going  on  the  same  ground 
twice  within  12  months.  The  time  of  grazing  during  freezing 
weather  would  not  be  included  in  such  a  plan,  as  few  of  the  eggs  or 
young  larvae  would  survive.  It  should  be  observed  that  it  is  not 
simply  the  changing  of  pastures  that  is  called  for,  but  changing  to 
clean  ground.  Putting  infested  sheep  on  pasture  in  May,  removing 
them  during  June  and  returning  them  in  July,  offers  an  excellent 
chance  for  infestation  from  the  eggs  dropped  during  the  first  pastur- 
ing which  would  have  hatched  out  into  young  worms  waiting  to  be 
taken  up. 

Some  modifications  of  such  a  plan  are  quite  practicable  on  any 
farm.  In  the  first  place,  the  danger  is  greatest  to  the  lambs,  and  after 
they  are  sold  or  separated  the  ewes  may  go  back  to  pastures  used 
earlier  in  the  season  with  much  less  danger  of  injury  than  would  be 
incurred  by  the  lambs.  This  change,  however,  would  render  that 
pasture  unsafe  for  young  lambs  during  the  following  spring.  Hay- 
fields,  grain  stubble,  and  cornfields  can  be  utilized  in  the  rotation  of 
fields  to  furnish  fresh  grazing. 


10     Department  Circular  47,  U.  S.  Department  of  Agriculture. 

Plowing  the  land  infested  with  the  larvae  of  stomach  worms  greatly 
reduces  the  danger  of  infection.  This  fact  allows  the  same  land  to  be 
used  two  or  three  times  for  sheep  in  a  season  by  using  forage  crops. 
Fall-sown  wheat  can  be  used  for  the  earliest  period,  the  land  broken 
and  resown  to  peas  and  oats,  rape,  or  soy  beans  for  a  later  grazing, 
and  in  some  cases  plowed  again  and  sown  to  wheat  to  furnish  late-fall 
feed.  A  succession  of  such  crops  is  particularly  desirable  for  carrying 
over  from  weaning  time  until  winter  the  ewe  lambs  that  are  to  be 
retained  in  the  flock. 

Where  sufficient  changes  of  pasture  and  fresh  ground  can  not  be 
provided,  preventive  dosing  may  be  partially  relied  upon.  The 
danger  in  depending  upon  treatment  lies  in  the  fact  that  while  cures 
usually  can  be  effected  by  its  proper  use,  lambs  that  have  been  al- 
lowed to  reach  the  point  where  medicine  is  needed  have  at  least  been 
seriously  checked  in  growth,  and  unless  very  carefully  watched  some 
deaths  will  occur. 

The  treatment  can  be  used  as  a  measure  to  hold  the  stomach 
worms  in  check,  in  conjunction  with  rotation  of  pastures.  Many 
successful  shepherds  dose  all  the  ewes  before  turning  them  on  the 
spring  pastures  with  the  lambs.  This  greatly  lessens  the  number  of 
eggs  dropped.  Afterwards  all  the  lambs  to  be  kept  are  similarly 
treated  at  the  time  of  weaning,  and  individual  cases  may  be  treated 
on  the  first  appearance  of  symptoms  which  will  be  noted  if  the  flock 
receives  the  attention  it  really  requires.  When  pasture  rotation  and 
similar  preventive  measures  are  impossible,  sheep  may  be  given  the 
copper-sulphate  treatment,  preferably  in  diminished  dosage,  every 
month  or  6  weeks  during  the  summer  season. 

The  stomach  worm  need  not  be  a  serious  trouble  for  a  good  shep- 
herd who  has  his  lambs  come  early,  feeds  well,  drenches  the  flock  as  a 
measure  of  prevention,  and  provides  a  rotation  of  pastures  or  pasture 
crops. 


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11 


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o 


>  »    O  •  9        • 


_» ^-r.,-1. 


xj-1 — i-^r* — * — • — *~ 


STOMACH  WORMS  IN  SHEEP 

PREVENTION  AND  TREATMENT 


Prepared  Jointly  by  the  Animal  Husbandry 
and  Zoological  Divisions 


UNITED  STATES  DEPARTMENT  OF  AGRICULTURE 
DEPARTMENT  CIRCULAR  47 


Contribution  from  the  Bureau  of  Animal  Industry 
JOHN  R.  MOHLER,  Chief 


Washington,  D.  C.  August,  1919 


WASHINGTON  :  GOVERNMENT  PRINTING  OFFICE  I  1919 


•    ■ 


STOMACH  WORMS  IN  SHEEP: 

PREVENTION  AND  TREATMENT. 


CONTENTS. 

Page. 

How  can  one  tell  when  sheep  have  stomach  worms  ? 3 

How  do  the  worms  injure  the  sheep ? 4 

How  should  infested  sheep  or  lambs  be  treated  ? 4 

How  do  sheep  become  infested  by  stomach  worms  ? 6 

What  methods  can  be  employed  to  prevent  loss  from  stomach  worms? 8 


ONE  of  the  most  serious  problems  of  owners  of  farm  sheep  is  the 
prevention  of  injury  and  loss  by  stomach  worms.  This  para- 
site (Hwmonclius  contortus)  has  been  known  in  this  country  for  many 
years  and  is  common  in  farm  flocks,  particularly  during  wet  summers. 
It  has  been  studied  by  the  Zoological  Division  of  the  Bureau  of 
Animal  Industry  and  the  principal  facts  in  its  life  history  have  been 
determined.  Methods  of  treatment  and  of  prevention  are  still  under 
investigation  by  that  division,  and  although  the  methods  have  not 
yet  been  perfected,  what  has  been  learned  is  sufficient  to  show  how 
affected  sheep  or  lambs  can  be  treated  successfully  and,  what  is  of 
greater  importance,  how  they  may  be  raised  in  such  a  way  as  practi- 
cally to  overcome  the  danger. 

What  is  known  of  this  parasite  and  the  methods  of  prevention  and 
control  may  be  presented  as  answers  to  practical  questions,  as 
follows : 

HOW  CAN  ONE  TELL  WHEN  SHEEP  HAVE  STOMACH  WORMS? 

Either  lambs  or  old  sheep  may  be  affected  by  stomach  worms  at 
any  time  of  the  year.  The  trouble  may  be  noticed  first  in  lambs 
about  the  middle  of  summer,  though  it  may  be  earlier,  according  to 
the  part  of  the  country  and  the  temperature  and  moisture  of  the 
season. 

In  many  flocks  the  first  knowledge  of  the  trouble  is  gained  through 
the  death  of  one  or  more  lambs.  If  the  flock  is  under  careful  obser- 
vation, however,  signs  of  stomach-worm  disease  will  be  noticed 
earlier.  Dullness  and  lack  of  thrift  are  among  the  first  indications. 
Scouring  is  often  present.  These  conditions  may  result  from  other 
causes,  but  when  due  to  stomach  worms,  they  are  accompanied  with  a 
very  pale,  bloodless  appearance  of  the  skin  and  of  the  mucous  mem- 
branes of  the  eyes  and  mouth.  The  whiteness  of  the  skin  has  caused 
the  trouble  to  be  known  in  some  sections  as  "paper  skin."  In  many 
cases  there  is  a  watery  swelling  under  the  jaws. 

120227°— 19  3 


4     Department  Circalor  kl \  U.  S.  Department  of  Agriculture. 

Doubt  as  to  the  cause  of  the  trouble  can  be  removed  by  an  exami- 
nation of  the  fourth  stomach.  For  examination  purposes,  any  one 
unfamiliar  with  the  ailment  can  well  afford  to  kill  an  affected  lamb. 
If  there  is  any  uncertainty  as  to  the  position  of  the  fourth  stomach 
it  can  be  ascertained  by  taking  hold  of  any  part  of  the  small  intestine 
and  following  it  forward.  The  fourth  stomach  is  one  of  the  4  com- 
partments into  which  the  stomach  is  divided  and  is  the  portion  con- 
tinuous with  the  forward  end  of  the  small  intestine.  When  the 
fourth  stomach  is  found,  it  should  be  held  so  as  to  prevent  the 
fluids  from  leaving  it  at  either  end,  and  an  incision  made  along 
nearly  the  full  length  of  the  upper  part.  When  this  is  done  the 
stomach  worms,  if  present,  can  be  seen,  often  in  large  numbers, 
wriggling  around  in  the  fluids.  They  are  from  one-half  to  \\  inches 
long,  about  as  thick  as  an  ordinary  pin,  and  spirally  striped  with 
red  and  white.  It  is  often  necessary  to  look  closely  for  some  time 
in  order  to  distinguish  them.  When  the  stomach  is  emptied  some 
of  the  worms  can  be  seen  adhering  to  the  inside  walls. 

HOW  DO  THE  WORMS  INJURE  THE  SHEEP? 

The  injurious  action  of  the  stomach  worms  may  be  attributed  to 
two  things:  First,  the  loss  of  blood  abstracted  by  the  parasites,  and 
second,  the  destruction  of  red  corpuscles  by  a  poisonous  substance 
which  is  secreted  by  the  parasites  and  taken  up  by  the  blood.  Evi- 
dently the  older,  stronger,  and  larger  sheep  are  better  able  than  the 
lambs  to  withstand  the  loss  of  blood,  and  can  better  endure  the  loss 
due  to  the  destruction  of  red  corpuscles.  Furthermore,  in  the  blood 
of  adult  sheep  there  may  be  substances  tending  to  neutralize  the 
poisonous  matter  produced  by  the  parasites  that  are  absent  from  the 
blood  of  lambs,  or  that,  if  present,  occur  in  smaller  quantities. 
Besides  the  direct  injury  caused  by  stomach  worms  it  is  not  unlikely 
that  damage  is  also  done  by  bacterial  infection  through  the  wounds 
the  worms  make  in  the  mucous  lining  of  the  stomach. 

HOW  SHOULD  INFESTED  SHEEP  OR  LAMBS  BE  TREATED? 

MEDICINAL  TREATMENT. 

If  taken  in  time,  most  cases  of  stomach  worms  can  bo  treated 
successfully  according  to  the  following  directions: 

Dissolve  one-fourth  pound  (avoirdupois)  of  the  powdered  crystals 
of  copper  sulphate  (bluestone)  in  1  pint  of  boiling  water,  using  a 
porcelain  or  enamel-ware  dish,  as  the  bluestone  corrodes  most  metals. 
Then  add  cold  water  enough  to  make  the  solution  up  to  3  gallons, 
using  wooden,  earthenware,  or  other  nonmetallic  receptacles.  This 
will  make  approximately  a  1  per  cent  solution  and  will  be  enough  to 
dose  100  adult  sheep,  allowing  10  per  cent  waste.  In  tho  preparation 
of  the  dose  use  only  clear-blue  crystals  of  copper  sulphate.  Crush 
tho  crystals  to  a  line  powder  when  ready  to  make  up  tho  solution. 


Stomach  Worms  in  Sheep.  5 

The  doses  for  lambs  and  sheep  are : 

For  lambs  under  1  year  of  age If  ouncea  (50  cubic  centimeters). 

For  sheep  past  1  year  old 3£  ounces  (100  cubic  centimeters). 

A  glass  with  marks  scratched  on  the  side  with  a  file  may  be  used 
for  measuring  the  doses. 

The  drenching  apparatus  consists  of  (1)  a  strong  rubber  tube 
about  3  feet  long  and  three-eighths  inch  in  diameter;  (2)  a  hard  rubber, 
porcelain,  or  enamel-ware  funnel,  which  is  fastened  to  one  end  of 
the  tube;  and  (3)  a  brass  mouthpiece  three-eighths  inch  in  diameter 
and  9  inches  long,  fastened  to  the  other  end.  It  is  preferable  that 
the  end  of  this  tube  should  be  closed  and  holes  made  in  the  sides  of 
about  the  last  two  inches  of  its  length. 

Ordinarily  the  treatment  is  given  after  the  sheep  have  been  without 
feed  overnight,  but  apparently  it  may  be  given  with  equally  good 
results  without  preliminary  fasting,  provided  the  animals  are  not 
gorged  with  feed  or  water  when  treated.  For  best  results  sheep 
should  not  be  watered  for  2  hours  afterwards. 

While  being  drenched  the  sheep  should  remain  on  all  4  legs  with 
its  head  held  horizontally.  This  is  important,  for  if  the  head  is 
held  above  the  horizontal  (nose  higher  than  the  eyes),  there  is  danger 
that  some  of  the  fluid  will  pass  into  the  lungs,  thereby  causing 
pneumonia  and  almost  certain  death.  Measure  the  dose  in  the 
measuring  glass,  and  after  the  drenching  tube  is  in  position  pour  the 
dose  slowly  into  the  funnel.  The  metal  mouthpiece  of  the  drenching 
tube  should  be  placed  between  the  jaws  in  the  space  between  the 
teeth  at  the  side  of  the  mouth  and  directed  backward,  but  should 
not  reach  farther  than  the  base  of  the  tongue.  In  order  to  prevent 
the  sheep  from  stopping  up  the  end  of  the  mouthpiece  with  its 
tongue  and  thus  interfering  with  the  flow  of  the  liquid,  the  person 
holding  the  mouthpiece  in  the  sheep's  mouth  should  give  it  a  rotary 
motion.  This  tends  to  keep  the  sheep  swallowing,  prevents  plugging 
the  tube,  and  also  tends  to  keep  the  fluid  from  entering  the  lungs. 
The  fluid  should  not  be  administered  more  rapidly  than  the  sheep 
can  swallow  comfortably. 

Care  in  the  administration  of  the  dose  is  highly  important,  as 
carelessness  or  any  undue  haste  is  liable  to  have  serious  results. 
The  copper-sulphate  treatment,  like  the  administration  of  medicines 
in  general,  is  safest  in  the  hands  of  a  competent  veterinarian. 

CHANGE  OF  PASTURE  NECESSARY  FOR  BEST  RESULTS. 

Although  losses  from  stomach  worms  in  many  cases  may  be 
minimized  by  repeated  medicinal  treatment  without  change  of 
pasture,  much  better  results  can  be  obtained  if  the  treated  animals 
are  placed  on  ground  that  is  free  or  practically  free  from  infection. 
It  is  still  better  to  institute  preventive  measures  before  the  results 
of  stomach-worm  infection  become  evident.     A  lamb  that  has  been 


6     Department  Circular  hi,  U.  S.  Department  of  Agriculture. 

affected  sufficiently  to  show  the  external  effects  of  stomach  worms 
has  received  a  serious  setback.  Although  it  may  recover  and  again 
be  thrifty  it  has  lost  at  least  a  month  or  6  weeks  of  progress  toward 
marketable  weight  and  condition.  The  only  safe  and  economical 
way  of  raising  sheep  where  stomach  worms  are  a  factor  is  by  managing 
the  flock  and  pastures  in  a  way  to  prevent  a  serious  develop- 
ment of  the  trouble.  In  most  localities  the  methods  necessary  for 
preventing  stomach  worms  are  at  the  same  time  those  that  need 
to  be  employed  for  most  economical  production.  In  order  to  follow 
these  methods,  particularly  with  respect  to  pasture  rotation,  the 
shepherd  needs  to  know  just  how  and  when  infection  occurs. 

HOW  DO  SHEEP  BECOME  INFESTED  BY  STOMACH  WORMS? 

INFESTED  PASTURES. 

In  the  adult  sexual  stage  stomach  worms  are  able  to  live  and 
carry  out  their  reproductive  functions  only  in  the  alimentary  canal 
of  sheep  or  other  ruminants,  and  practically  only  in  the  fourth  stom- 
ach. Each  female  produces  thousands  of  eggs,  of  microscopic  size, 
which  do  not  develop  into  adult  worms  in  the  body  of  the  host  in 
which  they  are  deposited,  but,  without  hatching,  pass  out  of  the 
intestine  in  the  feces.  In  a  few  hours,  days,  or  weeks,  according  as 
the  temperature  is  high  or  low,  these  eggs,  if  they  are  not  killed  by  dry- 
ing or  freezing  (either  of  which  is  commonly  fatal  to  them),  hatch  and 
the  tiny  embryonic  stomach  worms  then  develop  to  what  may  be 
termed  the  final  larval  or  infectious  stage.  This  later  development  like- 
wise requires  days  or  weeks,  according  to  the  temperature,  and  until 
the  young  worms  have  reached  the  infectious  stage  they  appear  to  be 
fully  as  susceptible  to  freezing  and  drying  as  the  eggs.  Having 
reached  the  infectious  stage,  however,  the  worms  are  able  to  with- 
stand long  periods  of  dryness  and  severe  cold,  though  some  of  them 
succumb  comparatively  early. 

In  the  infectious  stage  the  young  worms  are  very  active  in  the 
presence  of  moisture,  and  rapidly  crawl  up  blades  of  grass  and  other 
objects  whenever  the  relative  humidity  of  the  air  is  at  a  maximum, 
provided  the  temperature  is  above  40°  F.  or  thereabout;  below  that 
temperature  they  are  inactive.  A  decrease  in  the  relative  humidity, 
with  the  consequent  evaporation  of  the  moisture  from  tho  surface  of 
grass  blades  and  other  objects,  stops  the  migrations  of  the  worms, 
and  they  become  quiescent  and  remain  in  a  condition  of  suspended 
animation  wherever  they  happen  to  be  at  the  time.  During  the  next 
period  of  wet  weather,  dew,  rain,  or  fog,  tho  worms  again  become 
active  and  climb  still  higher  on  the  grass,  from  which  they  are  better 
able  to  attain  their  final  abode  within  the  stomach  of  a  sheep  or  cow 
than  if  they  remained  on  the  ground.  When  swallowed  by  a  sheep 
or  other  ruminant  the  young  stomach  worm,  if  it  has  reached  its  final 


Stomach  Worms  in  Sheep.  7 

larval  stage,  whether  active  at  the  time  or  in  a  state  of  suspended 
animation,  continues  its  development,  and  in  the  course  of  2  or  3 
weeks  reaches  maturity. 

The  length  of  life  of  individual  worms  in  the  stomach  has  not  been 
determined.  Infested  sheep  have  been  kept  in  pens  with  board 
floors,  which  were  kept  clean  by  sweeping  and  frequent  scrubbing — ■ 
the  sheep  being  fed  from  raised  racks  and  water  being  supplied  in  a 
trough  which  was  frequently  cleaned — for  varying  periods  up  to  a 
maximum  of  19  months,  and  at  the  end  of  these  periods  were  found 
to  be  still  infested,  though  the  number  of  worms  present  was  small. 

As  the  possibility  of  reinfection  by  larval  worms  developing  from 
eggs  passed  in  the  feces  of  these  sheep  was  not  entirely  removed, 
though  greatly  minimized,  the  results  obtained  do  not  necessarily 
indicate  that  the  worms  found  at  the  end  of  the  period  of  observation 
were  all  present  when  the  experiment  was  begun.  The  experiment, 
however,  while  it  proves  nothing  as  to  the  length  of  life  of  the  adult 
stomach  worm,  demonstrates  the  futility  of  attempting  to  rid  sheep 
entirely  of  stomach  worms  simply  by  keeping  them  away  from  pas- 
ture. On  the  other  hand,  very  little  infection  occurs  among  sheep 
kept  in  stables  if  cleanly  conditions  are  maintained.  Lambs  have 
been  kept  with  infested  sheep  in  stables  for  long  periods  of  time,  the 
only  precautions  against  infection  being  the  removal  of  manure  about 
once  a  week.  Under  such  conditions  they  have  continued  in  good 
health,  and  acquired  only  a  very  few  stomach  worms  and  other 
parasites. 

LENGTH  OF  TIME  PASTURES  MAY  BE  INFESTED. 

The  maximum  period  during  which  the  larval  stomach  worms  are 
able  to  survive  on  pastures  is  not  definitely  known,  but  it  has  been 
found  that  pastures  on  which  infested  sheep  had  grazed  were  appar- 
ently still  infectious  after  a  lapse  of  neariy  8  months,  namely,  from 
October  25,  when  the  infested  sheep  were  removed,  to  June  16,  when 
the  pastures  were  tested  by  placing  in  them  some  lambs  which  had 
been  raised  under  special  precautions  to  avoid  previous  infestation. 
In  cultures  made  September  14,  1906,  from  the  feces  of  an  infested 
sheep  and  kept  thereafter  in  the  laboratory,  most  of  the  larvae  were 
dead  but  some  were  still  alive,  though  very  sluggish,  on  June  5,  1907, 
nearly  9  months  later.  Cultures  in  which  the  worms  were  allowed 
to  develop  to  the  final  larval  stage,  after  they  were  kept  in  cold  storage 
at  a  temperature  below  freezing — in  some  cases  as  low  as  12°  F. — 
still  contained  some  living  worms  after  2  or  3  months,  while  in  other 
cultures  eggs  and  newly  hatched  worms  not  yet  developed  to  the  final 
larval  stage  were  killed  within  a  few  hours  after  exposure  to  tempera- 
tures below  freezing. 

These  experiments  show  that  pastures  may  remain  infected  for 
several  months  after  sheep  are  removed  from  them,  and  that  the 


8     Department  Circular  47,  U.  S.  Department  of  Agriculture. 

infection  is  not  destroyed  by  cold  weather.  They  show,  however, 
that  during  a  winter  with  more  or  less  freezing  weather  there  is 
likely  to  be  little  or  no  increase  in  the  amount  of  infection  in  pastures 
occupied  by  infested  sheep.  The  eggs  passed  in  the  feces  of  the  sheep 
will  either  be  killed  at  onoe  by  freezing,  or,  on  account  of  low  tem- 
peratures above  freezing,  will  remain  dormant  or  develop  so  slowly 
that  they  are  killed  later  by  frost  before  they  have  reached  the  final 
larval  stage,  which  is  resistant  to  cold.  At  the  same  time,  while  the 
infestation  of  pastures  may  not  be  increased  during  the  winter,  the 
infestation  of  the  sheep  may  be  added  to  by  their  picking  up  from 
time  to  time  larval  worms  which,  prior  to  the  beginning  of  cold 
weather,  had  developed  already  to  the  stage  in  which  they  are  able 
to  withstand  freezing. 

If  sheep,  goats,  and  cattle  are  kept  off  a  pasture  for  a  year,  it  is 
fair  to  assume,  upon  the  basis  of  our  present  knowledge,  that  all,  or 
practically  all,  larval  stomach  worms  will  have  died  within  that  time. 
There  is  also  little  doubt  that  the  period  required  for  the  practical 
disinfection  of  a  pasture  may  be  shortened  considerably  by  plowing 
it  and  placing  it  under  cultivation. 

Thus  there  are  two  ways  by  which  a  pasture  may  be  freed  of  infesta- 
tion, one  by  excluding  sheep  or  other  ruminants  for  at  least  a  year,  and 
the  other  by  turning  it  into  a  cultivated  field.  In  view  of  the  fact 
that  sheep  placed  on  disinfected  fields  or  pastures  probably  will  not 
be  entirely  free  from  infestation,  it  is  not  of  much  consequence 
whether  every  larval  stomach  worm  in  the  pastures  is  dead  or  not. 
The  approximation  to  this  point,  which  is  attained  by  vacating  pas- 
tures for  a  year  or  by  plowing  them  up,  is  sufficient  for  practical 
purposes. 

WHAT  METHODS  CAN  BE  EMPLOYED  TO  PREVENT  LOSS  FROM 

STOMACH  WORMS? 

It  is  barely  possible  that  some  means  of  artificially  producing  in 
lambs  an  immunity  against  the  evil  effects  of  stomach  worms  may 
be  devised,  but  at  the  present  time  it  is  only  a  matter  for  speculation 
and  experimental  research.  Our  present  knowledge  of  the  stomach 
worm  leads  us  to  direct  our  efforts  toward  bringing  about  freedom 
from  infestation  or,  as  the  next  best  thing,  reducing  the  amoimt  of 
infestation  to  a  minimum  and  keeping  it  there. 

EARLY  DEVELOPMENT  OF  LAMBS. 

One  great  step  toward  evading  the  stomach  worm  is  found  in  the 
plan  of  having  lambs  dropped  early  and  feeding  to  develop  them  as 
much  as  possible  before  they  go  to  pasture. 

Where  sheep  graze  during  winter  and  spring  there  is  little  danger 
of  infestation  in  freezing  weather,  as  the  eggs  or  young  larva*  are  killed 


Stomach  Worms  in  Sheep.  9 

before  they  are  taken  up  by  the  lambs.  There  is  but  very  slight 
danger  that  young  lambs  will  become  affected  seriously  while  running 
with  older  sheep  in  barns  or  yards  free  from  vegetation.  Early  lamb- 
ing, combined  with  good  feeding  of  the  ewes  to  make  them  milk  well, 
or  of  the  lambs  themselves  in  a  "creep,"  or  with  both,  brings  early 
lambs  to  marketable  weight  and  finish  before  the  most  dangerous 
part  of  the  summer.  Where  lambs  must  remain  for  several  months 
on  pasture,  frequent  changing  of  pasture  must  be  resorted  to,  to 
keep  infestation  below  the  extent  that  is  injurious. 

A  PRACTICABLE  METHOD  OF  PASTURE  ROTATION. 

The  means  of  preventing  the  stomach-worm  larvae  from  getting 
into  the  lambs  is  suggested  by  what  has  been  said  concerning  its 
development  and  powers  of  resistance.  It  was  stated  that  a  pasture 
that  had  been  occupied  by  wormy  sheep  would  need  to  be  for  at 
least  a  year  without  cattle,  sheep,  or  goats  in  order  to  become 
practically  free  from  stomach-worm  larvae. 

From  10  to  20  days,  according  to  temperature  and  moisture,  must 
intervene  between  the  dropping  of  the  feces  containing  stomach- 
worm  eggs  and  the  development  of  many  of  the  larvae  to  a  point 
where  they  will  develop  into  adult  worms  after  being  swallowed.  If 
sheep  are  moved  to  a  fresh  pasture  before  the  eggs  in  their  droppings 
develop  into  mature  larvae,  complete  health  can  be  maintained.  The 
practical  difficulty  lies  in  always  having  a  fresh  pasture  available. 
If  only  permanent  grass  pasture  were  used,  adequate  control  would 
call  for  as  many  separate  pastures  as  would  allow  the  flock  to  be 
moved  at  least  every  2  weeks  without  going  on  the  same  ground 
twice  within  12  months.  The  time  of  grazing  during  freezing 
weather  would  not  be  included  in  such  a  plan,  as  few  of  the  eggs  or 
young  larvae  would  survive.  It  should  be  observed  that  it  is  not 
simply  the  changing  of  pastures  that  is  called  for,  but  changing  to 
clean  ground.  Putting  infested  sheep  on  pasture  in  May,  removing 
them  during  June  and  returning  them  in  July,  offers  an  excellent 
chance  for  infestation  from  the  eggs  dropped  during  the  first  pastur- 
ing which  would  have  hatched  out  into  young  worms  waiting  to  be 
taken  up. 

Some  modifications  of  such  a  plan  are  quite  practicable  on  any 
farm.  In  the  first  place,  the  danger  is  greatest  to  the  lambs,  and  after 
they  are  sold  or  separated  the  ewes  may  go  back  to  pastures  usod 
earlier  in  the  season  with  much  less  danger  of  injury  than  would  be 
incurred  by  the  lambs.  This  change,  however,  would  render  that 
pasture  unsafe  for  young  lambs  during  the  following  spring.  Hay- 
fields,  grain  stubble,  and  cornfields  can  be  utilized  in  the  rotation  of 
fields  to  furnish  fresh  grazing. 


10     Department  Circular  47,  U.  S.  Department  of  Agriculture. 

Plowing  the  land  infested  with  the  larvae  of  stomach  worms  greatly 
reduces  the  danger  of  infection.  This  fact  allows  the  same  land  to  be 
used  two  or  three  times  for  sheep  in  a  season  by  using  forage  crops. 
Fall-sown  wheat  can  be  used  for  the  earliest  period,  the  land  broken 
and  resown  to  peas  and  oats,  rape,  or  soy  beans  for  a  later  grazing, 
and  in  some  cases  plowed  again  and  sown  to  wheat  to  furnish  late-fall 
feed.  A  succession  of  such  crops  is  particularly  desirable  for  carrying 
over  from  weaning  time  until  winter  the  ewe  lambs  that  are  to  be 
retained  in  the  flock. 

Where  sufficient  changes  of  pasture  and  fresh  ground  can  not  be 
provided,  preventive  dosing  may  be  partially  relied  upon.  The 
danger  in  depending  upon  treatment  lies  in  the  fact  that  while  cures 
usually  can  be  effected  by  its  proper  use,  lambs  that  have  been  al- 
lowed to  reach  the  point  where  medicine  is  needed  have  at  least  been 
seriously  checked  in  growth,  and  unless  very  carefully  watched  some 
deaths  will  occur. 

The  treatment  can  be  used  as  a  measure  to  hold  the  stomach 
worms  in  oheok,  in  conjunction  with  rotation  of  pastures.  Many 
successful  shepherds  dose  all  the  ewes  before  turning  them  on  the 
spring  pastures  with  the  lambs.  This  greatly  lessens  the  number  of 
eggs  dropped.  Afterwards  all  the  lambs  to  be  kept  are  similarly 
treated  at  the  time  of  weaning,  and  individual  cases  may  be  treated 
on  the  first  appearance  of  symptoms  which  will  be  noted  if  the  flock 
receives  the  attention  it  really  requires.  When  pasture  rotation  and 
similar  preventive  measures  are  impossible,  sheep  may  be  given  the 
copper-sulphate  treatment,  preferably  in  diminished  dosage,  every 
month  or  6  weeks  during  the  summer  season. 

The  stomaoh  worm  need  not  be  a  serious  trouble  for  a  good  shep- 
herd who  has  his  lambs  come  early,  feeds  well,  drenches  the  flock  as  a 
measure  of  prevention,  and  provides  a  rotation  of  pastures  or  pasture 
crops. 


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PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION. 

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Cerebrospinal  Meningitis.     (Department  Bulletin  65.) 

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11 


12   Department  Circular  47,  U.  S.  Department  of  Agriculture. 

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o 


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